As an energy source that does not cause environmental pollution, a fuel cell is attracting attention and researches thereof are actively done in recent years. A fuel cell directly generates electricity by electrochemically reacting hydrogen and oxygen. A fuel cell is basically composed of, as a unit, a power generation cell wherein a membrane electrode assembly is held by being sandwiched between a separator having a groove to be a flow path of a fuel gas (hydrogen gas) and a separator comprising groove to be a flow path of oxygen (air) gas. Here, the membrane electrode assembly consists of an electrolyte membrane, a fuel electrode arranged on one surface of the electrolyte membrane, and an oxygen electrode arranged on the other surface of the electrolyte membrane. A separator comprising a groove to be a flow path of a fuel gas (hydrogen gas) takes the role of flowing the fuel gas (hydrogen gas), such that the fuel gas (hydrogen gas), which is fed into a power generation cell from the outside, comes into contact with the surface of the fuel electrode, passes thereon and is then exhausted to the outside of the power generation cell. A separator comprising a groove to be a flow path of an oxygen (air) gas takes the role of flowing the oxygen (air) gas, such that the oxygen (air) gas, which is fed into a power generation cell from the outside, comes into contact with the surface of the fuel electrode, passes thereon and is then exhausted to the outside of the power generation cell. Basically, a fuel cell consists of one power generation cell. However, when high output power generation is performed, a plurality of power generation cells are stacked one upon another to constitute one fuel cell. A fuel cell composed of such plural power generation cells stacked one upon another is generally referred to as a fuel cell stack.
As mentioned above, a separator in a fuel cell sections gas flow paths of a fuel gas and an oxygen gas, and therefore, is required to have gas impermeability and corrosion resistance hard to deteriorate even if exposed to a gas. A separator is required to have electroconductivity, because it takes the role of a power collection electrode to collect the electric current generated in a power generation layer and to take it outside, besides the role of a gas flow path. Thus, as a separator for fuel cells, one obtained by applying press working on a plate (board) comprising conductive materials such as metal, carbon and the like or one obtained by applying cutting work such as end mill, fraise and the like on the plate (board) to form a groove to be a gas flow path, as shown in, for example, JP-A-10-125337 and JP-A-2000-36309 is generally employed.
However, it is difficult to make conventional separators thinner. This is because a plate requires a certain thickness in consideration of maintenance of processability (processing stability) during press working or cutting work of a metal plate, a carbon plate and the like. As a result, conventional fuel cells thicken naturally, which particularly makes it difficult to form a thin fuel cell. As a separator with the use of a metal plate, one using a plate of, for example, pure copper, stainless steel and the like is typical. However, since a separator with the use of a metal plate not only becomes heavier but is associated with the defects in that it is deteriorated by a long term contact with a hydrogen gas to be used as a fuel gas, cutting work and etching processing for groove formation are needed, thus increasing the number of steps and the cost, and when it is made thin, plastic deformation occurs, thus making shape retention difficult. In contrast, while a graphite plate is superior in gas impermeability and lightweight, it is expensive and requires a long time for the production of the graphite plate itself. Therefore, it is inferior in the productivity. Moreover, since processing of graphite plate requires slice cutting with a diamond cutter, the number of steps and the cost increase. Moreover, since a graphite plate has a high hardness, it easily gets broken when made thin.